The present invention relates to processes for creping a cellulosic web and to paper wiping products prepared thereby.
Absorbent paper products such as paper towels, industrial wipers, and the like generally are designed to have high bulk, a soft feel, and high absorbency. Desirably, these paper wiping products will exhibit high strength, even when wet, and resist tearing. Further, such products should have good stretch characteristics, should be abrasion resistant, and should not prematurely deteriorate in the environment in which they are used.
In the past, many attempts have been made to enhance certain physical properties of paper wiping products. Unfortunately, steps taken to increase one property often adversely affect other characteristics. For example, in pulp fiber-based wiping products, softness may be increased by inhibiting or reducing interfiber bonding within the paper web. Inhibiting or reducing fiber bonding, however, adversely affects the strength of the product.
One process which has proven successful in producing paper towels and other wiping products is disclosed in U.S. Pat. No. 3,879,257 to Gentile et al., which patent is incorporated herein by reference in its entirety. Gentile et al. disclose a process for producing a soft, absorbent, single ply fibrous web having a laminate-like structure. The fibrous web is formed from an aqueous slurry of primarily lignocellulosic fibers under conditions which reduce interfiber bonding. A bonding material, such as a latex elastomeric composition, is applied to a first surface of the web in a spaced-apart pattern. The bonding material provides strength to the web and abrasion resistance to the surface. The bonding material may be applied in a like manner to a second surface of the web to provide additional strength and abrasion resistance. After applying bonding material to the second surface, the web may be brought into contact with a creping surface, such as the cylinder surface of a Yankee dryer. The bonding material will cause the web to adhere to the creping surface. The web then is creped from the creping surface with a doctor blade. Creping the web mechanically debonds and disrupts the fibers within the web, except where bonding material is present, thereby increasing the softness, absorbency, and bulk of the web. If desired, both sides of the web may be creped sequentially after the pattern of bonding material has been applied.
Gentile et al. describe the optional use in the process of one or more curing or drying stations before the web is wound into what is referred to as a parent roll. As a practical matter, curing or drying is necessary in order to prevent the layers in the parent roll from sticking or adhering to one another (a phenomenon referred to in the art as "blocking"). Moreover, unless the web is cooled before it is wound into the parent roll, spontaneous combustion may occur. As is well known by those having ordinary skill in the art, drying is an energy-intensive step, particularly when two curing or drying stations are employed. The presence of curing or drying stations also adds to the capital cost of the process equipment. Similarly, the need for a cooling station or chill roll adds to both capital and operating costs.
The presence of curing or drying stations also limits the types of noncellulosic fibers which may be present in the web. Such stations typically are operated at temperatures of the order of 150.degree. C. These temperatures preclude the presence in the web of synthetic polymer fibers prepared from, by way of example only, polyolefins.
Thus, there is a need for a creping process which would permit the development of sufficient strength and other desirable attributes without an energy-intensive curing step. There also is a need for a creping process which would permit the use of a wider variety of synthetic polymeric fibers.